(1) Field of the Invention
The present invention relates to a method and apparatus for estimating an estimated voltage that is an estimated terminal voltage of a battery, which supplies the electric power to loads in a vehicle, in its constant load discharging state, a method and apparatus for computing an open circuit voltage corresponding to a terminal voltage of the battery in its equilibrium state, and a method and apparatus for computing a charging capacity of the battery. More specifically, the present invention relates to a method and apparatus for estimating an estimated voltage that is an estimated terminal voltage of a battery in its constant load discharging state, in which a voltage-current characteristic derived from a periodically measured terminal voltage and discharge current of the battery is used, a method and apparatus for computing an open circuit voltage and charging capacity of the battery from the estimated voltage.
(2) Description of the Related Art
So far, a driving source of a vehicle has been mainly an engine, in which gasoline or gas oil is employed as the fuel, but in recent years a vehicle employing an electromotive motor, which does not directly discharge the combustion gas, as the only or the supplementary driving source has appeared. As to a vehicle loading the electromotive motor, grasping a charging capacity of a battery, which supplies the electric power to the electromotive motor, is important for computing a possible traveling distance and so on.
So far, an integration method of current or electric power has been employed, in which an integrated consumed electric power computed by using an integrated value of the discharge current is subtracted from a full charging capacity so as to compute the present charging capacity. However, in such a method, an original full charging capacity is changed depending upon individual differences among batteries, deterioration rates of the batteries and so on, therefore the present charging capacity of the battery cannot be accurately computed.
A state of charge of the battery can be known by measuring the density of the electrolyte of the battery since there is a certain linear relationship between the density of the electrolyte and the state of charge. However, actually in a battery during charging or discharging and a battery right after the completion of charge or discharge thereof, chemical reactions occurring between the electrolyte and the electrodes make the density of the electrolyte non-uniform, therefore the state of charge of the battery cannot be known accurately by measuring the density of the electrolyte.
Besides, the charging capacity of the battery may be known by measuring the terminal voltage of the battery. But the terminal voltage is not stable unless the discharge current is stabilized, therefore actually the terminal voltage correlating with the state of charge of the battery cannot be obtained by the measurement.
As shown in characteristic graphs in FIG. 22, in which the battery is subjected to the discharge with each constant current ranging from 10 to 80 A in units of 10 A, the discharging time (horizontal axis) increases with decreasing the discharge current while the terminal voltage (vertical axis) of the battery drastically decreases with the discharging time.
Here, the horizontal axis of the characteristic graphs in FIG. 22 is the time, however, since the discharge is carried out with the constant current and the battery capacity is expressed by electrical quantity (Ah), this horizontal axis can be regarded as the battery capacity.
Then, the characteristic graphs in FIG. 22 reveals that smaller the discharge current, higher the electric power to be obtained and that the capacity drop near the state of full charge of the battery is slow while the capacity drop near the state of full discharge is rapid.
As described above, even if the discharge current can be stabilized, since there is no linear correlation between the charging capacity of the battery and the terminal voltage thereof, the charging capacity cannot be derived from the terminal voltage of the battery.
Thus, appears to be reasonable is a method for computing the capacity employing a relationship between the state of charge of the battery and the open circuit voltage, which is possibly a linear relationship since there is about a linear relation between the electrolyte density of the battery and the open circuit voltage and since there is a linear relation between the electrolyte density of the battery and the state of charge of the battery.
However, the sole weak point of this method for computing the capacity is that the open circuit voltage can be measured during non-discharging period of time when the state of charge of the battery does not change, except the self-discharging. In other words, the open circuit voltage cannot be measured during discharging when the state of charge of the battery changes.
Consequently, a point of the above method for computing the capacity is how to find out the open circuit voltage during the discharge of the battery.
The terminal voltage and the discharge current can be measured during the discharge of the battery. As shown in FIG. 22, since the terminal voltage appears to decrease with increasing the discharge current even when the state of charge of the battery does not change, there is a voltage-current characteristic (I-V characteristic) showing a negative correlation between the terminal voltage and the discharge current, which changes with changing the state of charge of the battery.
Thus, in order to know a plurality of the voltage-current characteristics of the battery in response to the state of charge of the battery, the following measurement is carried out.
First, a discharge is continuously carried out by using an impulse current, in which a current Ia and a current Ib smaller than Ia are periodically mutually appear, and then the predetermined number of the sets (for example, 100 sets) of the terminal voltage having a reverse phase with respect to the discharge current and the discharge current, i.e. (Ia, V1), (Ib, V2), (Ia, V3), (Ib, V4), - - - are continuously sampled at the same period of time with the impulse cycle (for example, 1 millisecond) of the discharge current.
Then, from thus sampled sets of the terminal voltage and the discharge current, i.e. (Ia, V01), (Ib, V02), (Ia, V03), (Ib, V04), - - - , by using the method of least squares, coefficients a1 and b1 in an equation V=a1I+b1, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=a1I+b1 is placed as the voltage-current characteristic of the battery corresponding to the capacity during the above sampling.
Then, the similar discharge to the discharge described above is continuously carried out by using an impulse current, in which currents Ia and Ia are periodically mutually appear, and then the predetermined number of the sets of the terminal voltage having a reverse phase with respect to the discharge current and the discharge current, i.e. (Ia, V11), (Ib, V12), (Ia, V13), (Ib, V14), - - - are continuously sampled. Then, from thus sampled sets of the terminal voltage and the discharge current, by using the method of least squares, coefficients a2 and b2 in an equation V=a2I+b2, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=a2I+b2 is placed as the voltage-current characteristic of the battery corresponding to the capacity during the above sampling.
Thereafter, similarly, coefficients an and bn in an equation V=anI+bn, i.e. a linear relationship between the voltage and current of the battery are obtained, wherein the equation V=anI+bn is placed as the voltage-current characteristic of the battery corresponding to each mutually different capacity which gradually decreases, thereby the voltage-current characteristics of the battery corresponding to the respective capacities ranging from 100% to 0%.
In FIG. 23, there is schematically shown a relation between the sampled sets of the terminal voltage and the discharge current. i.e. (Ia, Vn1), (Ib, Vn2), (Ia, Vn3), (Ib, Vn4), - - - and the linear voltage-current equation V=anI+bn, which is obtained from the sets by using the method of least squares.
Here, an imaginary current value Is that is an imaginary constant current value is substituted to the voltage-current characteristic equation of the battery corresponding to the respective capacities, then if the resultant obtained V is defined as an estimated voltage Vn that is an estimated terminal voltage of the battery in its state of constant-load discharge, a constant current discharging characteristic shown in graphs in FIG. 24 is obtained.
When any positive value is substituted for the imaginary current value Is, the corresponding constant current discharging characteristic becomes a non-linear characteristic, in which the estimated terminal voltage Vn rapidly decreases as the capacity of the horizontal axis increases in the vicinity of the right end of the respective curves, and even in the case of the imaginary current value Is=0 A, in which the open circuit voltage must be theoretically shown, the constant current discharging characteristic shows a similar characteristic.
According to the graphs in FIG. 24, since smaller the imaginary current value Is, smaller the degree of decreasing in the estimated voltage Vn as the capacity reduces to zero, therefore when a negative value is substituted as the imaginary current value Is to the voltage-current characteristic equation of the battery corresponding to the respective capacities, the resultant constant current discharging characteristic is expressed by curves shown in FIG. 25. In this case, the characteristic of the estimated voltage Vn in the vicinity of the capacity being zero shows an inflectional change having a boundary of the imaginary current value Is=xe2x88x9210 A.
Consequently, theoretically if the imaginary current value Is is set to be xe2x88x9210 A, the estimated voltage Vn in the constant current discharge shows a linear relationship with respect to the capacity of the battery.
FIG. 26 shows graphs illustrating the voltage-current characteristic of the battery corresponding to the respective capacities with having the vertical axis of the discharge current I and the horizontal axis of the terminal voltage V. In the following, that the estimated voltage Vn during the constant current discharging has a linear relationship with respect to the battery capacity will be verified.
Since coefficients a1, a2, - - - , an, expressing the respective gradients of the voltage-current characteristic equations are mutually different and coefficients b1, b2 - - - , bn expressing the respective intercepts of the voltage-current characteristic equations also are mutually different, in the region of positive discharge current that actually exists, no value I of discharge current, at which the terminal voltage V linearly changes with the change in the battery capacity, exists.
To the contrary, in the region of negative discharge current that is an imaginary region shown in FIG. 26, the terminal voltage V shows a characteristic of changing linearly with respect to the battery capacity, that is, the terminal voltage V of the battery corresponding to each capacity at the discharge current value I=xe2x88x9210 A is the estimated voltage Vn.
A graph in FIG. 27 shows a relationship between the battery capacity at the imaginary current value Is=xe2x88x9210 A and the estimated voltage Vn that has a linear correlation with the battery capacity. As shown in FIG. 16, the estimated voltage Vn exists between the open circuit voltage Vs at the fully charged state and the open circuit voltage Ve at the end of discharge, therefore a capacity value corresponding to the estimated voltage Vn is a residual capacity, i.e. a state of charge (SOC).
Consequently, since the estimated voltage takes the place of the open circuit voltage of the battery, even upon discharge when the open circuit voltage cannot be measured, provided that the discharge is a constant load discharge, in which the load supplying the electric power does not change during discharge, the terminal voltage that changes delicately during discharge and the discharge current are measured, thereby the voltage-current characteristic that is a relation between the terminal voltage and the discharge current during the constant load discharge is known. Then, the imaginary current value Is=xe2x88x9210 A is substituted into the resultant characteristic equation (V=aI+b) so as to know the estimated voltage Vn, thereby the a state of charge (SOC) of the battery can be calculated from the estimated voltage Vn.
The present state of charge (SOC) with respect to the fully charged capacity can be calculated from the graph shown in FIG. 27 as follows:
SOC={(VnVe)(Vsxe2x88x92Ve)}xc3x97100(%). 
More accurately, the present state of charge (SOC) with respect to the fully charged capacity can be calculated as follows in terms of a ratio of the electric power (Vxc3x97Ah):                     SOC        =                  xe2x80x83                ⁢                  {                                    [                                                (                                      Vn                    +                    Ve                                    )                                ⁢                2                            ]                        xc3x97                          [                                                (                                      Vn                    -                    Ve                                    )                                ⁢                                  (                                      Vs                    -                    Ve                                    )                                            ]                        xc3x97            A            ⁢                          xe2x80x83                        ⁢            h            }                                                            xe2x80x83                ⁢                              {                                          [                                                      (                                          Vs                      +                      Ve                                        )                                    ⁢                  2                                ]                            xc3x97              A              ⁢                              xe2x80x83                            ⁢              h                        }                    xc3x97          100          ⁢                      xe2x80x83                    ⁢                      (            %            )                                                  =                  xe2x80x83                ⁢                              {                                          (                                                      Vn                    2                                    -                                      Ve                    2                                                  )                            ⁢                              (                                                      Vs                    2                                    -                                      Ve                    2                                                  )                                      }                    xc3x97          100          ⁢                      xe2x80x83                    ⁢                                    (              %              )                        .                              
Generally, as shown in FIG. 28, during the discharge of a battery, a voltage drop due to a pure resistance (ohmic resistance of the battery) such as IR drop (=the pure resistances discharge current) and a voltage drop due to a polarization at the discharging side takes place, on the other hand during the charge of the battery, a voltage rise due to the pure resistance such as voltage rise due to a polarization at the charging side takes place.
Especially as shown in FIG. 28, an activation polarization for advancing redox reactions on the surface of the electrodes, which is included in the polarization at the discharging side arising during the discharge of the battery, and a concentration polarization due to the difference in concentrations of the reactants and products generated from a result of the mass transfer between the electrode surfaces and the solution, take place with some delay with respect to the increase and decrease in the discharge current, therefore the polarization does not show a linear relationship with the value of the discharge current.
Consequently, when the estimated voltage Vn is to be calculated instead of the open circuit voltage in order to compute the state of charge (SOC) of the battery, the terminal voltage and the discharge current are measured during the discharge so as to calculate the voltage-current characteristic. However, since the terminal voltage includes the voltage drop due to the polarization during the discharge, the calculated voltage-current characteristic and the estimated voltage Vn calculated therefrom include the voltage drop due to the polarization besides the state of charge (SOC) of the battery, therefore the estimated voltage Vn as it cannot be employed to calculate accurately the state of charge (SOC) of the battery.
Further, since the amount of the voltage drop due to the polarization varies depending upon the amount of the discharge current and the length of the discharging period of time required for the discharge current to reach its maximum value after the discharge is started, when the discharge current value or the discharge time varies, a gradient in the voltage-current characteristic of the battery that is calculated from the measured values of the terminal voltage and the discharge current during discharge changes, in response thereto.
Furthermore, the estimated voltage Vn estimated from the voltage-current characteristic, the charging state SOC of the battery calculated from the estimated voltage Vn, or each value of the non-measurable open circuit voltage OCV, which may be calculated prior to the charging state SOC, also can be a different value depending upon the difference in the discharge current value or the discharge time.
It is therefore an objective of the present invention to solve the above problem and to provide a method and apparatus for estimating an estimated voltage that is an estimated terminal voltage of a battery in its constant load discharging state, a method and apparatus for computing an open circuit voltage corresponding to a terminal voltage of the battery in its equilibrium state, and a method and apparatus for computing a charging capacity of the battery, wherein the open circuit voltage and charging capacity of the battery are computed from the estimated voltage, and the estimation of the estimated voltage of the battery and the computation of the open circuit voltage or the charging capacity of the battery can be accurately carried out, even if the amount of the voltage drop included in the terminal voltage of the battery during the discharge thereof varies depending upon the discharge current value or the discharge time.
In order to attain the above objective, the present invention is to provide a method for estimating a terminal voltage of a battery comprising the steps of:
periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current; and
estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic,
wherein when the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic including an influence of a polarization is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured while the discharge current of the constant load discharge decreases from the maximum current value,
the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery, and
a voltage value corresponding to a predetermined imaginary current value in the voltage-current characteristic including the influence of the polarization shifted in the direction of the voltage coordinate axis is estimated as a value of the estimated voltage.
With the construction described above, once the discharge current of the constant load discharge reaches the current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to a discharge current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the discharge current value, newly arises after the residual voltage rise is canceled.
On the other hand, even if the battery in an equilibrium state carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, when the discharge current reaches the discharge current value, the polarization arises, the magnitude of which corresponds to the discharge current value.
Therefore, when the battery carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, not depending upon that the battery was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery while the discharge current is decreasing from the discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, is the same.
The magnitude of the polarization arisen in the battery during the discharge depends on the discharge current value and the discharge period of time required for the discharge current to reach the maximum value thereof.
Therefore, if the discharge period of time for the discharge current to reach the maximum value thereof after the start of the discharge is long, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge becomes larger than that when the discharge period of time is short even if the maximum value of the discharge current is the same. On the other hand, if the maximum value of the discharge current is large, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge becomes larger than that when the maximum value of the discharge current is small even if the discharge period of time is the same.
Further, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge increases with almost the same pace as that of the discharge current increasing while the discharge current increases, however when the discharge current once reaches the maximum value thereof and starts decreasing, the voltage drop value of the terminal voltage decreases with a pace slower than that of the discharge current decreasing, as a result, the greater part of the voltage drop value of the terminal voltage due to the polarization is not canceled for a while even after the discharge is finished and the discharge current becomes zero accordingly.
Summarizing the characteristics described above, when the voltage-current characteristic including the influence of the polarization, which shows the correlation between the terminal voltage and discharge current, is computed from the terminal voltage and discharge current measured during the discharge, the difference in the voltage drop value depending on the discharge current value and the discharge period of time significantly affects the characteristic during the increase of the discharge current and hardly affects the characteristic during the decrease of the discharge current.
Consequently, out of the voltage-current characteristic including the influence of the polarization, as for the characteristic during the increase of the discharge current, the characteristic itself changes depending on the discharge current value and the discharge period of time. On the other hand, as for the characteristic during the decrease of the discharge current, the characteristic itself hardly changes even when the discharge current value and the discharge period of time change, that is, only a parameter value indicating an intercept on a voltage coordinate axis in a general equation indicating the characteristic changes and only a terminal voltage value corresponding to a discharge current value changes.
Therefore, out of the voltage-current characteristic including the influence of the polarization of the battery, which is computed by measuring the discharge current and terminal voltage during the discharge, the characteristic itself during the decrease of the discharge current does not change if the discharge current value and the discharge period of time change.
Therefore, when the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic including an influence of a polarization is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured while the discharge current of the constant load discharge decreases from the maximum current value, and
the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery. Thereby, the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current is pumped up (raised up) in the direction of a voltage coordinate axis by a factor of a voltage drop value due to the polarization, the generated amount of which increases due to the increase of the discharge current, as a result, the variable component by the discharge current value and the discharge period of time of the voltage-current characteristic during the increase of the discharge current is removed from the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current.
Preferably, the voltage-current characteristic including the influence of the polarization is expressed by an approximate curve equation.
With the construction described above, the low pace of the decrease in the voltage drop value of the terminal voltage, which is arisen in the battery due to the polarization by the discharge, is more correctly reflected in the voltage-current characteristic including the influence of the polarization, thereby the accuracy of the estimated voltage estimated on the basis of the voltage-current characteristic including the influence of the polarization becomes higher.
Preferably, the current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge is set to be a predetermined large current value required to drive a maximum power consuming load independently out of the loads in the vehicle, which receive an electric power from the battery, and
after the discharge current of the battery starts decreasing from the predetermined large current value, while the discharge current of the battery is lower than the predetermined large current value and is decreasing up to a target current value that is higher than a maximum discharge current value when the loads in the vehicle except the maximum power consuming load are driven, a voltage-current characteristic including an influence of a polarization for the battery in an equilibrium state thereof and the voltage-current characteristic including the influence of the polarization are calculated from the periodically measured terminal voltage and discharge current of the battery.
With the construction described above, the predetermined large current value required to drive the maximum power consuming load independently out of the loads in the vehicle exceeds each current value used for driving the other load even if a plurality of powers are simultaneously supplied to the other loads. Therefore, the predetermined large current value is set to be a current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, thereby when the discharge current reaches the predetermined large current value, a voltage drop exceeding the voltage drop due to the discharge-side polarization arisen by the former discharge is already arisen in the terminal voltage of the battery.
On the other hand, when the discharge current value of the battery decreases from the predetermined large current value and reaches to a target current value not less than a maximum discharge current value when the loads except the maximum power consuming load are driven, a voltage drop component due to the discharge-side polarization arisen by the power supply to the loads in the vehicle except the maximum power consuming load does not seemingly affect the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery, but a remaining component except a component removed by that the discharge current decreases to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value seemingly affects the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery.
Consequently, the voltage-current characteristic including the influence of the polarization is computed from the terminal voltage and the discharge current periodically measured while the discharge current of the battery, which has carried out the constant load discharge with the predetermined large current value, starts decreasing from the predetermined large current value and reaches the target current value. A present estimated voltage estimated on the basis of the voltage-current characteristic including the influence of the polarization purely reflects only the remaining component except the component canceled due to the decrease of the discharge current decreasing up to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value, even if the loads in the vehicle except the maximum power consuming load are still driven.
The present invention is also to provide a method for computing an open circuit voltage of a battery comprising the steps of:
periodically measuring a terminal voltage and a discharge current of a battery that supplies an electric power to loads in a vehicle;
calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current;
estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic; and
computing an open circuit voltage of the battery corresponding to a terminal voltage of the battery in an equilibrium state thereof on the basis of the estimated voltage,
wherein when the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic including an influence of a polarization is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured while the discharge current of the constant load discharge decreases from the maximum current value,
the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery,
a difference value between the open circuit voltage value at the current being zero in the voltage-current characteristic not including the influence of the polarization and the estimated voltage value estimated on the basis of the voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis is in advance calculated as a residual voltage drop value due to an influence of a residual polarization upon a completion of the discharge of the battery,
thereafter, whenever the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic including the influence of the polarization is newly calculated from the terminal voltage and the discharge current of the battery periodically measured during the constant load discharge,
the newly calculated voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so that a voltage value at the reference current value in the newly calculated voltage-current characteristic including the influence of the polarization agrees with the reference voltage value in the voltage-current characteristic not including the influence of the polarization when the voltage-current characteristic including the influence of the polarization is newly calculated,
a present estimated voltage is estimated on the basis of the newly calculated voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis, and
a present open circuit voltage is computed by adding the residual voltage drop value to the present estimated voltage value.
With the construction described above, when the discharge current of the constant load discharge of the battery reaches a current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, even if a voltage drop or voltage rise due to the polarization of the discharge-side or the charge-side arisen in the former discharge remains before the discharge starts, the battery becomes in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value arises or in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value newly arises after canceling the residual voltage rise.
On the other hand, even if the battery has carried out the constant load discharge with a current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, when the current value reaches the discharge current value, the battery becomes in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value.
Therefore, when the battery carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, not depending upon that the battery was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery while the discharge current is decreasing from the discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, is the same.
Then, not depending on whether or not the battery has been in an equilibrium state before the start of the constant load discharge with the discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, the estimated voltage value estimated after the battery starts the constant load discharge is lower than an open circuit voltage corresponding to the terminal voltage of the battery in the equilibrium state thereof when the battery before the start of the constant load discharge has been supposed in an equilibrium state, by a residual voltage drop value in advance calculated as the residual voltage drop value due to the residual polarization at the end of the constant load discharge.
The magnitude of the polarization arisen in the battery during the discharge depends on the discharge current value and the discharge period of time required for the discharge current to reach the maximum value thereof.
Therefore, if the discharge period of time for the discharge current to reach the maximum value thereof after the start of the discharge is long, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge becomes larger than that when the discharge period of time is short even if the maximum value of the discharge current is the same. On the other hand, if the maximum value of the discharge current is large, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge becomes larger than that when the maximum value of the discharge current is small even if the discharge period of time is the same.
Further, the voltage drop value of the terminal voltage arisen in the battery due to the polarization due to the discharge increases with almost the same pace as that of the discharge current increasing while the discharge current increases, however when the discharge current once reaches the maximum value thereof and starts decreasing, the voltage drop value of the terminal voltage decreases with a pace slower than that of the discharge current decreasing, as a result, the greater part of the voltage drop value of the terminal voltage due to the polarization is not canceled for a while even after the discharge is finished and the discharge current becomes zero accordingly.
Summarizing the characteristics described above, when the voltage-current characteristic including the influence of the polarization, which shows the correlation between the terminal voltage and discharge current, is computed from the terminal voltage and discharge current measured during the discharge, the difference in the voltage drop value depending on the discharge current value and the discharge period of time significantly affects the characteristic during the increase of the discharge current and hardly affects the characteristic during the decrease of the discharge current.
Consequently, out of the voltage-current characteristic including the influence of the polarization, as for the characteristic during the increase of the discharge current, the characteristic itself changes depending on the discharge current value and the discharge period of time. On the other hand, as for the characteristic during the decrease of the discharge current, the characteristic itself hardly changes even when the discharge current value and the discharge period of time change, that is, only a parameter value indicating an intercept on a voltage coordinate in a general equation indicating the characteristic changes and only a terminal voltage value corresponding to a discharge current value changes.
Therefore, out of the voltage-current characteristic including the influence of the polarization of the battery, which is computed by measuring the discharge current and terminal voltage during the discharge, the characteristic itself during the decrease of the discharge current does not change if the discharge current value and the discharge period of time change.
Therefore, when the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic including an influence of a polarization is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured while the discharge current of the constant load discharge decreases from the maximum current value, and
the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery. Thereby, the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current is pumped up (raised up) in the direction of a voltage coordinate axis by a factor of a voltage drop value due to the polarization, the generated amount of which increases due to the increase of the discharge current, as a result, the variable component by the discharge current value and the discharge period of time of the voltage-current characteristic during the increase of the discharge current is removed from the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current.
Therefore, a difference value between
the estimated voltage value estimated on the basis of the voltage-current characteristic including the influence of the polarization after shifted in the direction of a voltage coordinate axis so that the voltage value at the reference current value in advance calculated as a residual voltage drop value, which is the residual voltage drop due to the residual polarization at the end of the discharge when the battery has carried out the constant load discharge agrees with the reference voltage value on the voltage-current characteristic not including the influence of the polarization and
the open circuit voltage value that is a voltage value when the current is zero in the voltage-current characteristic not including the influence of the polarization
does not include a variable component of the voltage-current characteristic due to the difference in the discharge current or in the discharge period of time.
In other words, the open circuit voltage value that is a voltage value when the current is zero in the voltage-current characteristic not including the influence of the polarization corresponds to the terminal voltage of the battery in an equilibrium state thereof when supposing that the battery has been in the equilibrium state before the start of the constant load discharge. Therefore, if the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so as to intersect at the reference value on the voltage-current characteristic not including the influence of the polarization, the estimated voltage estimated from the shifted voltage-current characteristic including the influence of the polarization is always lower than the open circuit voltage by the residual voltage drop value.
Preferably, after the residual voltage drop value is calculated, whenever the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge, the voltage-current characteristic not including the influence of the polarization is calculated when the voltage-current characteristic including the influence of the polarization is newly calculated from the terminal voltage and the discharge current of the battery periodically measured during the constant load discharge.
With the construction described above, when the voltage-current characteristic including the influence of the polarization is computed from the terminal voltage and discharge current of the battery periodically measured during the constant load discharge of the battery, the voltage-current characteristic not including the influence of the polarization is also computed from the terminal voltage and discharge current periodically measured, thereby it is used for computing the present open circuit voltage.
Preferably, whenever the battery becomes in an equilibrium state thereof, the terminal voltage value of the battery measured in the equilibrium state thereof is obtained as a present open circuit voltage value,
a newest voltage-current characteristic not including the influence of the polarization is calculated from the terminal voltage and the discharge current of the battery, which are periodically measured when the battery carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge starting from the equilibrium state,
a newest voltage-current characteristic including the influence of the polarization is calculated from the terminal voltage and the discharge current of the battery periodically measured while a discharge current of the constant load discharge, which the battery carries out with a current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge starting from the equilibrium state, is decreasing from a predetermined large current value,
a newest residual voltage drop value is calculated on the basis of the obtained terminal voltage value and the newest voltage-current characteristic including the influence of the polarization, and
thereafter, the present open circuit voltage is computed on the basis of the newest residual voltage drop value and the newest voltage-current characteristic not including the influence of the polarization.
With the construction described above, whenever the battery becomes in an equilibrium state the terminal voltage of the battery is measured and the measured value is obtained as a present open circuit voltage value. Thereafter, when the battery in the equilibrium state carries out the constant load discharge, a newest residual voltage drop value is computed on the basis of a newest voltage-current characteristic including the influence of the polarization computed from the periodically measured terminal voltage and discharge current of the battery and the terminal voltage of the battery in the equilibrium newly obtained as a present open circuit voltage value, thereby the residual voltage drop value to be used for computing the present open circuit voltage value is renewed to a newest value.
Further, when the battery in the equilibrium state carries out the constant load discharge with the current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, a newest voltage-current characteristic not including the influence of the polarization is computed from the terminal voltage and discharge current periodically measured, thereby the voltage-current characteristic not including the influence of the polarization, which is used for computing the residual voltage drop value and the present open circuit voltage, is renewed to a newest characteristic.
Preferably, the voltage-current characteristic including the influence of the polarization is expressed by an approximate curve equation.
With the construction described above, the low pace of the decrease in the voltage drop value of the terminal voltage, which is arisen in the battery due to the polarization by the discharge, is more correctly reflected in the voltage-current characteristic including the influence of the polarization, thereby the accuracy of the estimated voltage estimated on the basis of the voltage-current characteristic including the influence of the polarization and the accuracy of the open circuit voltage computed by using the estimated voltage become higher.
Preferably, the current value large enough to cancel a charge-side polarization arisen in the battery at least just before the discharge is set to be a predetermined large current value required to drive a maximum power consuming load independently out of the loads in the vehicle, which receive an electric power from the battery, and
after the discharge current of the battery starts decreasing from the predetermined large current value, while the discharge current of the battery is lower than the predetermined large current value and is decreasing up to a target current value that is higher than a maximum discharge current value when the loads in the vehicle except the maximum power consuming load are driven, a voltage-current characteristic including an influence of a polarization for the battery in an equilibrium state thereof and the voltage-current characteristic including the influence of the polarization are calculated from the periodically measured terminal voltage and discharge current of the battery.
With the construction described above, the predetermined large current value required to drive the maximum power consuming load independently out of the loads in the vehicle exceeds each current value used for driving the other load even if a plurality of powers are simultaneously supplied to the other loads. Therefore, the predetermined large current value is set to be a current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, thereby when the discharge current reaches the predetermined large current value, a voltage drop exceeding the voltage drop due to the discharge-side polarization arisen by the former discharge is already arisen in the terminal voltage of the battery.
On the other hand, when the discharge current value of the battery decreases from the predetermined large current value and reaches to a target current value not less than a maximum discharge current value when the loads except the maximum power consuming load are driven, a voltage drop component due to the discharge-side polarization arisen by the power supply to the loads in the vehicle except the maximum power consuming load does not seemingly affect the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery, but a remaining component except a component removed by that the discharge current decreases to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value seemingly affects the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery.
Consequently, the voltage-current characteristic including the influence of the polarization is computed from the terminal voltage and the discharge current periodically measured while the discharge current of the battery, which has carried out the constant load discharge with the predetermined large current value, starts decreasing from the predetermined large current value and reaches the target current value. A present estimated voltage estimated on the basis of the voltage-current characteristic including the influence of the polarization purely reflects only the remaining component except the component canceled due to the decrease of the discharge current decreasing up to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value, even if the loads in the vehicle except the maximum power consuming load are still driven.
Preferably, whenever a present estimated voltage of the battery is estimated on the basis of the voltage-current characteristic including the influence of the polarization shifted in the direction of the voltage coordinate axis, the residual voltage drop value is revised in response to an inside or circumferential temperature of the battery upon the estimation and another inside or circumferential temperature of the battery when the voltage-current characteristic not including the influence of the polarization for the battery in the equilibrium state thereof is obtained, and the present open circuit voltage is computed from the revised residual voltage drop value.
With the construction described above, when the inside or circumferential temperature of the battery changes, the battery capacity changes and the terminal voltage of the battery also changes. Therefore, if the inside or circumferential temperature of the battery is different from each other between when the voltage-current characteristic not including the influence of the polarization to be used for computing the residual voltage drop value is obtained and when the present estimated voltage is estimated from the voltage-current characteristic including the influence of the polarization computed during the constant load discharge, a component of the terminal voltage reflected in the residual voltage drop value in response to the inside or circumferential temperature of the battery is different from a component of the terminal voltage reflected in the present estimated voltage in response to the inside or circumferential temperature of the battery.
However, if the residual voltage drop value is revised in response to the inside or circumferential temperature of the battery when the voltage-current characteristic not including the influence of the polarization is obtained and the inside or circumferential temperature of the battery when the present estimated voltage is estimated from the voltage-current characteristic including the influence of the polarization, which is computed during the constant load discharge, the component of the terminal voltage responding to the inside or circumferential temperature of the battery is reflected in the residual voltage drop value and in the estimated voltage under the same condition, therefore if the revised residual voltage drop value is used, the present open circuit voltage can be computed in a state that the variable component of the terminal voltage due to the difference of the inside or circumferential temperature of the battery is removed.
The present invention is also to provide a method for computing a battery capacity comprising the step of computing a present charging capacity of the battery from the present open circuit voltage computed by the method for computing an open circuit voltage of a battery as described above.
With the construction described above, the present open circuit voltage not including the dispersion due to the difference in the discharge current value or the discharge period of time caused by the voltage fluctuation due to the polarization is used, thereby a present charging capacity of the battery, which has a linear relationship with the open circuit voltage, can be computed without including the influence of the voltage fluctuation due to the polarization.
A method for computing the voltage-current characteristic not including the influence of the polarization of the battery or a method for computing the voltage-current characteristic not including the influence of the polarization of the battery in an equilibrium state thereof is not limited to a specific method. Some examples for such a method will be explained as follows.
As for a first method, on the basis of the terminal voltage and discharge current periodically measured when the battery carries out the constant load discharge with a current value large enough to cancel the charge-side polarization arisen at least just before the discharge, a first approximate curve equation of the voltage-current characteristic indicating a correlation between the terminal voltage and the discharge current of the battery during the increase of the discharge current and a second approximate curve equation of the voltage-current characteristic indicating a correlation between the terminal voltage and the discharge current of the battery during the decrease of the discharge current are computed. Then, a first point is defined on the voltage-current characteristic curve expressed by the first approximate curve equation while a second point is defined on the voltage-current characteristic curve expressed by the second approximate curve. Then, a first imaginary point having the same resistance value as a second combined resistance consisting of a pure resistance of the battery and a second polarization resistance component, which causes a second voltage drop when a second discharge current corresponding to the second point flows, is imaged on the voltage-current characteristic curve expressed by the first approximate curve equation, while a second imaginary point having the same resistance value as a first combined resistance consisting of a pure resistance of the battery and a first polarization resistance component, which causes a first voltage drop when a first discharge current corresponding to the first point flows, is imaged on the voltage-current characteristic curve expressed by the second approximate curve equation. Then, a first gradient of a straight line defined by connecting the second point and the first imaginary point is revised by a quantity corresponding to a voltage drop difference due to the second polarization resistance component arising from the second discharge current and a discharge current at the first imaginary point, thereby a first revised gradient excluding the contribution of the voltage drop due to the second polarization resistance component is computed, while a second gradient of a straight line defined by connecting the first point and the second imaginary point is revised by a quantity corresponding to a voltage drop difference due to the first polarization resistance component arising from the first discharge current and a discharge current at the second imaginary point, thereby a second revised gradient excluding the contribution of the voltage drop due to the first polarization resistance component is computed. Finally, an average gradient is computed by addition-averaging the first and second gradients, thereby the average gradient is computed as the pure resistance of the battery, that is, the voltage-current characteristic not including the influence of the polarization of the battery.
With the first method described above, the pure resistance of the battery can be computed only by processing data of the terminal voltage and discharge current of the battery periodically measured during the constant load discharge with the predetermined large current.
As for a second method, in addition to the first method described above, the first and second points may be set as an optional point in a range where the terminal voltage and the discharge current of the battery, which are measured in order to compute the first and second approximate curve equations, exist.
With the second method described above, at least one point for computing the gradient is based on real data, therefore a point significantly missing the real conditions is prevented from being used.
As for a third method, in addition to the first or second method described above, the first and second points may be set as a point corresponding to the maximum current value of the discharge current of the battery, which is measured in order to compute the first and second approximate curve equations, on the first and second approximate curve equations.
With the third method described above, at least one point for computing the gradient is based on real data, therefore a point significantly missing the real conditions is prevented from being used and in addition, since both points are common, an error is prevented from entering compared to a case, in which the different data are used.
As for a fourth method, in addition to the first, second or third method described above, when the first and second approximate curve equations are computed, the periodically measured terminal voltage and discharge current of the battery may be collected for the newest predetermined period of time and stored.
With the fourth method described above, by using the stored real data, the first and second approximate curve equations can be computed after confirming that the discharge current required to compute the first and second approximate curve equations has flowed.
As shown in FIG. 1, the present invention is also to provide an apparatus for estimating a terminal voltage of a battery executing the steps of: periodically measuring a terminal voltage and a discharge current of a battery 13 that supplies an electric power to loads in a vehicle; calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current; and estimating an estimated voltage that is an estimated terminal voltage of the battery in a constant load discharging state thereof from the voltage-current characteristic,
the apparatus comprising:
first computing means 23A for computing a voltage-current characteristic including an influence of a polarization from a terminal voltage and a discharge current of the battery 13 periodically measured after the discharge current of the battery 13 starts decreasing from a maximum current value, in a constant load discharge that the battery 13 carries out with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge,
second computing means 23B for computing a voltage-current characteristic including an influence of a polarization shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery 13, when the first computing means 23A computes the voltage-current characteristic including the influence of the polarization, and
estimating means 23C for estimating a voltage value corresponding to a predetermined imaginary current value in the voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis computed by the second computing means 23B is estimated as a present value of the estimated voltage of the battery 13.
With the construction described above, as shown in FIG. 1, once the discharge current of the constant load discharge reaches the current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, even if the voltage drop or rise due to the polarization at the charge or discharge side arisen in the former discharge remains before the start of the discharge, the system is in a state that the polarization of the discharge side corresponding to a discharge current value, which exceeds the residual voltage drop, arises or in a state that the polarization of the discharge side, the magnitude of which corresponds to the discharge current value, newly arises after the residual voltage rise is canceled.
On the other hand, even if the battery 13 in an equilibrium state carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, when the discharge current reaches the discharge current value, the polarization arises, the magnitude of which corresponds to the discharge current value.
Therefore, when the battery 13 carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, not depending upon that the battery 13 was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery 13 while the discharge current is decreasing from the discharge current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, is the same.
The magnitude of the polarization arisen in the battery 13 during the discharge depends on the discharge current value and the discharge period of time required for the discharge current to reach the maximum value thereof.
Therefore, if the discharge period of time for the discharge current to reach the maximum value thereof after the start of the discharge is long, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge becomes larger than that when the discharge period of time is short even if the maximum value of the discharge current is the same. On the other hand, if the maximum value of the discharge current is large, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge becomes larger than that when the maximum value of the discharge current is small even if the discharge period of time is the same.
Further, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge increases with almost the same pace as that of the discharge current increasing while the discharge current increases, however when the discharge current once reaches the maximum value thereof and starts decreasing, the voltage drop value of the terminal voltage decreases with a pace slower than that of the discharge current decreasing, as a result, the greater part of the voltage drop value of the terminal voltage due to the polarization is not canceled for a while even after the discharge is finished and the discharge current becomes zero accordingly.
Summarizing the characteristics described above, when the voltage-current characteristic including the influence of the polarization, which shows the correlation between the terminal voltage and discharge current, is computed from the terminal voltage and discharge current measured during the discharge, the difference in the voltage drop value depending on the discharge current value and the discharge period of time significantly affects the characteristic during the increase of the discharge current and hardly affects the characteristic during the decrease of the discharge current.
Consequently, out of the voltage-current characteristic including the influence of the polarization, as for the characteristic during the increase of the discharge current, the characteristic itself changes depending on the discharge current value and the discharge period of time. On the other hand, as for the characteristic during the decrease of the discharge current, the characteristic itself hardly changes even when the discharge current value and the discharge period of time change, that is, only a parameter value indicating an intercept on a voltage coordinate in a general equation indicating the characteristic changes and only a terminal voltage value corresponding to a discharge current value changes.
Therefore, after detecting means A for detecting the start of the decrease of the discharge current detects that the discharge current of the battery 13 starts decreasing from the predetermined large current value, as for the voltage-current characteristic including the influence of the polarization, which is computed by the first computing means 23A from the periodically measured terminal voltage and discharge current of the battery 13, the characteristic equation thereof itself does not change even if the discharge current value or the discharge period of time changes.
Therefore, if the second computing means 23B shifts the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery 13, when the first computing means 23A computes the voltage-current characteristic including the influence of the polarization, the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current is pumped up (raised up) in the direction of a voltage coordinate axis by a factor of a voltage drop value due to the polarization, the generated amount of which increases due to the increase of the discharge current, as a result, the variable component by the discharge current value and the discharge period of time of the voltage-current characteristic during the increase of the discharge current is removed from the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current.
Preferably, the first computing means 23A computes the voltage-current characteristic including the influence of the polarization as an approximate curve equation.
With the construction described above, the low pace of the decrease in the voltage drop value of the terminal voltage, which is arisen in the battery 13 due to the polarization by the discharge, is more correctly reflected in the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A, thereby the accuracy of the estimated voltage estimated by the estimating means 23C on the basis of the voltage-current characteristic including the influence of the polarization becomes higher.
Preferably, the current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge is a predetermined large current value required to drive a maximum power consuming load 5 independently out of the loads in the vehicle, which receive an electric power from the battery 13, and
after the discharge current of the battery 13 starts decreasing from the predetermined large current value, while the discharge current of the battery 13 is decreasing up to a target current value that is higher than a maximum discharge current value when the loads in the vehicle except the maximum power consuming load 5 are driven, the first computing means 23A computes the voltage-current characteristic including the influence of the polarization from the periodically measured terminal voltage and discharge current of the battery 13.
With the construction described above, the predetermined large current value required to drive the maximum power consuming load independently out of the loads in the vehicle exceeds each current value used for driving the other load even if a plurality of powers are simultaneously supplied to the other loads. Therefore, the predetermined large current value is set to be a current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, thereby when the discharge current reaches the predetermined large current value, a voltage drop exceeding the voltage drop due to the discharge-side polarization arisen by the former discharge is already arisen in the terminal voltage of the battery 13.
On the other hand, when the discharge current value of the battery 13 decreases from the predetermined large current value and reaches to a target current value not less than a maximum discharge current value when the loads except the maximum power consuming load are driven, a voltage drop component due to the discharge-side polarization arisen by the power supply to the loads in the vehicle except the maximum power consuming load does not seemingly affect the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery 13, but a remaining component except a component removed by that the discharge current decreases to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value seemingly affects the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery 13.
Consequently, the voltage-current characteristic including the influence of the polarization is computed by the first computing means 23A from the terminal voltage and the discharge current periodically measured while the discharge current of the battery 13, which has carried out the constant load discharge with the predetermined large current value, starts decreasing from the predetermined large current value and reaches the target current value. A present estimated voltage estimated by the estimating means 23C on the basis of the voltage-current characteristic including the influence of the polarization purely reflects only the remaining component except the component canceled due to the decrease of the discharge current decreasing up to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value, even if the loads in the vehicle except the maximum power consuming load are still driven.
The present invention is also to provide an apparatus for computing an open circuit voltage of a battery 13 executing the steps of: periodically measuring a terminal voltage and a discharge current of a battery 13 that supplies an electric power to loads in a vehicle; calculating a voltage-current characteristic expressing a correlation between the terminal voltage and the discharge current; estimating an estimated voltage that is an estimated terminal voltage of the battery 13 in a constant load discharging state thereof from the voltage-current characteristic; and computing an open circuit voltage of the battery 13 corresponding to a terminal voltage of the battery 13 in an equilibrium state thereof on the basis of the estimated voltage,
the apparatus comprising:
storing means 27 for storing a residual voltage drop value due to a residual polarization upon a completion of the discharge when the battery 13 carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge;
first computing means 23A for computing the voltage-current characteristic including an influence of a polarization from the periodically measured terminal voltage and discharge current of the battery 13 after the discharge current of the battery starts decreasing from a maximum current value, during the constant load discharge that the battery 13 carries out with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge;
second computing means 23B for computing a voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization, which is computed by the first computing means 23A, agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery, when the first computing means 23A computes the voltage-current characteristic including the influence of the polarization; and
estimating means 23C for estimating a present estimated voltage of the battery 13 on the basis of the voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis computed by the second computing means 23B,
wherein the storing means 27 in advance stores a difference value between
a value of the estimated voltage in advance estimated on the basis of an in advance computed voltage-current characteristic including the influence of the polarization sifted in the direction of a voltage coordinate axis, which is obtained by shifting the in advance computed voltage-current characteristic including the influence of the polarization in the direction of the voltage coordinate axis, so that a voltage value at the reference current value in the in advance computed voltage-current characteristic including the influence of the polarization agrees with the reference voltage value in the in advance computed voltage-current characteristic not including the influence of the polarization and
a value of the open circuit voltage at the current being zero in the in advance computed voltage-current characteristic not including the influence of the polarization,
and a present open circuit voltage is computed by adding the residual voltage drop value in advance stored by the storing means to the present estimated voltage value estimated by the estimating means.
With the construction described above, when the discharge current of the constant load discharge of the battery 13 reaches a current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, even if a voltage drop or voltage rise due to the polarization of the discharge-side or the charge-side arisen in the former discharge remains before the discharge starts, the battery 13 becomes in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value arises or in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value newly arises after canceling the residual voltage rise.
On the other hand, even if the battery 13 has carried out the constant load discharge with a current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, when the current value reaches the discharge current value, the battery 13 becomes in a state that a discharge-side polarization having the magnitude corresponding to the discharge current value.
Therefore, when the battery 13 carries out a constant load discharge with a discharge current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, not depending upon that the battery 13 was in an equilibrium state before the start of the constant load discharge or that the polarized state at the discharge or charge side arisen in the former discharge is not quite completely canceled, the estimated voltage estimated from the voltage-current characteristic, which is calculated from the discharge current and the terminal voltage of the battery 13 while the discharge current is decreasing from the discharge current value large enough to cancel the charge-side polarization arisen in the battery at least just before the discharge, is the same.
Then, not depending on whether or not the battery 13 has been in an equilibrium state before the start of the constant load discharge with the discharge current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, the estimated voltage value estimated after the battery 13 starts the constant load discharge is lower than an open circuit voltage corresponding to the terminal voltage of the battery 13 in the equilibrium state thereof when the battery 13 before the start of the constant load discharge has been supposed in an equilibrium state, by a residual voltage drop value in advance calculated and stored by the storing means 27 as the residual voltage drop value due to the residual polarization at the end of the constant load discharge.
The magnitude of the polarization arisen in the battery 13 during the discharge depends on the discharge current value and the discharge period of time required for the discharge current to reach the maximum value thereof.
Therefore, if the discharge period of time for the discharge current to reach the maximum value thereof after the start of the discharge is long, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge becomes larger than that when the discharge period of time is short even if the maximum value of the discharge current is the same. On the other hand, if the maximum value of the discharge current is large, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge becomes larger than that when the maximum value of the discharge current is small even if the discharge period of time is the same.
Further, the voltage drop value of the terminal voltage arisen in the battery 13 due to the polarization due to the discharge increases with almost the same pace as that of the discharge current increasing while the discharge current increases, however when the discharge current once reaches the maximum value thereof and starts decreasing, the voltage drop value of the terminal voltage decreases with a pace slower than that of the discharge current decreasing, as a result, the greater part of the voltage drop value of the terminal voltage due to the polarization is not canceled for a while even after the discharge is finished and the discharge current becomes zero accordingly.
Summarizing the characteristics described above, when the voltage-current characteristic including the influence of the polarization, which shows the correlation between the terminal voltage and discharge current, is computed from the terminal voltage and discharge current measured during the discharge, the difference in the voltage drop value depending on the discharge current value and the discharge period of time significantly affects the characteristic during the increase of the discharge current and hardly affects the characteristic during the decrease of the discharge current.
Consequently, out of the voltage-current characteristic including the influence of the polarization, as for the characteristic during the increase of the discharge current, the characteristic itself changes depending on the discharge current value and the discharge period of time. On the other hand, as for the characteristic during the decrease of the discharge current, the characteristic itself hardly changes even when the discharge current value and the discharge period of time change, that is, only a parameter value indicating an intercept on a voltage coordinate in a general equation indicating the characteristic changes and only a terminal voltage value corresponding to a discharge current value changes.
Therefore, after detecting means A for detecting the start of the decrease of the discharge current detects that the discharge current of the battery 13 starts decreasing from the predetermined large current value, as for the voltage-current characteristic including the influence of the polarization, which is computed by the first computing means 23A from the periodically measured terminal voltage and discharge current of the battery 13, the characteristic equation thereof itself does not change even if the discharge current value or the discharge period of time changes.
Therefore, if the second computing means 23B shifts the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A in the direction of a voltage coordinate axis so that a voltage value at a reference current value lower than the maximum current value in the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A agrees with a reference voltage value at the reference current value in the voltage-current characteristic, which does not include the influence of the polarization but depends only on a pure resistance component of the battery 13, when the first computing means 23A computes the voltage-current characteristic including the influence of the polarization, the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current is pumped up (raised up) in the direction of a voltage coordinate axis by a factor of a voltage drop value due to the polarization, the generated amount of which increases due to the increase of the discharge current, as a result, the variable component by the discharge current value and the discharge period of time of the voltage-current characteristic during the increase of the discharge current is removed from the voltage-current characteristic including the influence of the polarization during the decrease of the discharge current.
Therefore, a difference value between
the estimated voltage value for the battery 13 that has been in an equilibrium estimated from the shifted voltage-current characteristic including the influence of the polarization for the battery 13 that has been in an equilibrium, which is stored by the storing means 27 as the residual voltage drop value that is the residual voltage drop quantity due to the residual polarization at the end of the discharge when the battery 13 has carried out the constant load discharge with a current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge and
the open circuit voltage value that is a voltage value when the current is zero in the voltage-current characteristic not including the influence of the polarization for the battery 13 in an equilibrium thereof
does not include a variable component of the voltage-current characteristic due to the difference in the discharge current or in the discharge period of time.
In other words, the open circuit voltage value that is a voltage value when the current is zero in the voltage-current characteristic not including the influence of the polarization corresponds to the terminal voltage of the battery 13 in an equilibrium state thereof when supposing that the battery 13 has been in the equilibrium state before the start of the constant load discharge. Therefore, if the voltage-current characteristic including the influence of the polarization is shifted in the direction of a voltage coordinate axis so as to intersect at the reference value on the voltage-current characteristic not including the influence of the polarization, the estimated voltage estimated from the shifted voltage-current characteristic including the influence of the polarization is always lower than the open circuit voltage by the residual voltage drop value.
Preferably, the apparatus for computing an open circuit voltage of a battery further comprises third computing means 23D for computing the voltage-current characteristic not including the influence of the polarization from the periodically measured terminal voltage and discharge current of the battery 13, which carries out a constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge, wherein the second computing means 23B computes the voltage-current characteristic including the influence of the polarization shifted in the direction of a voltage coordinate axis on the basis of the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A and the voltage-current characteristic not including the influence of the polarization computed by the third computing means 23D.
With the construction described above, after the discharge current of the battery 13 starts decreasing from the current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, when the first computing means 23A computes the voltage-current characteristic including the influence of the polarization from the periodically measured terminal voltage and discharge current of the battery 13, the third computing means 23D computes the voltage-current characteristic not including the influence of the polarization at that time from the terminal voltage and discharge current of the battery 13 periodically measured while the battery 13 carries out the constant load discharge with the current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge. Then, the second computing means 23B computes the shifted voltage-current characteristic including the influence of the polarization on the basis of the voltage-current characteristic not including the influence of the polarization computed by the third computing means 23D and the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A.
Preferably, the apparatus for computing an open circuit voltage of a battery further comprises:
judging means 23E for judging whether or not the battery 13 is in an equilibrium state thereof,
measuring means A for measuring a terminal voltage of the battery 13 when the battery 13 is judged to be in an equilibrium state thereof by the judging means 23E;
calculating means 23F for calculating the newest residual voltage drop value by subtracting the present estimated voltage value estimated by the estimating means 23C on the basis of the terminal voltage and discharge current of the battery 13, which is judged in an equilibrium state thereof by the judging means 23E, periodically measured while the battery 13 carries out the constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge from a terminal voltage value of the battery 13 most newly measured by the measuring means A;
renewing means 23G for renewing the residual voltage drop value stored by the storing means 27 to the newest residual voltage drop value calculated by the calculating means 23F; and
fourth computing means 23H for computing a newest voltage-current characteristic not including the influence of the polarization on the basis of the terminal voltage and discharge current of the battery 13, which is judged in an equilibrium state thereof by the judging means 23E, periodically measured while the battery 13 carries out the constant load discharge with a current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge.
With the construction described above, whenever the judging means 23E judges that the battery 13 is in an equilibrium state, the terminal voltage of the battery 13 is measured by means A for measuring the terminal voltage in the equilibrium state of the battery. Thereafter, the present estimated voltage value estimated by the estimating means from the periodically measured terminal voltage and discharge current is subtracted from the terminal voltage value of the battery 13 in the equilibrium state thereof, which is most newly measured by means A for measuring the terminal voltage in the equilibrium state of the battery, thereby the calculating means 23F calculates the newest residual voltage drop value, then the renewing means 23G renews the residual voltage drop value stored by the storing means 27 to the newest residual voltage drop value calculated by the calculating means 23F.
Further, when the battery, which is judged in the equilibrium state by the judging means 23E, carries out the constant load discharge with the current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, a newest voltage-current characteristic not including the influence of the polarization is computed by the fourth computing means 23H from the terminal voltage and discharge current periodically measured, thereby the voltage-current characteristic not including the influence of the polarization, which is used for computing the residual voltage drop value and the present open circuit voltage, is renewed to a newest characteristic, similarly to the residual voltage drop value renewed to the newest value thereof by the renewing means 23G.
Preferably, the apparatus for computing an open circuit voltage of a battery 13 further comprises:
detecting means 19 for detecting an inside or circumferential temperature of the battery 13; and
revising means 23J for revising the residual voltage drop value stored by the storing means 27 in response to an inside or circumferential temperature of the battery 13 detected by the detecting means 19 when the estimating means 23C estimates the present estimated voltage and another inside or circumferential temperature of the battery 13 detected by the detecting means 19 when the renewing means 23G renews the residual voltage drop value stored by the storing means 27 to the newest residual voltage drop value calculated by the calculating means 23F,
wherein the present open circuit voltage is computed by adding the residual voltage drop value revised by the revising means 23J to the estimated voltage value estimated by the estimating means 23C.
With the construction described above, since when the inside or circumferential temperature of the battery 13 changes the battery capacity changes and terminal voltage also changes, therefore if the inside or circumferential temperature of the battery 13 detected by the detecting means 19 is different from each other between when the renewing means 23G renews the residual voltage drop value stored by the storing means 27 to the newest residual voltage drop value and when the estimating means 23C estimates the present estimated voltage of the battery 13, a terminal voltage component reflected in the residual voltage drop value in response to the inside or circumferential temperature of the battery 13 is different from a terminal voltage component reflected in the estimated voltage in response to the inside or circumferential temperature of the battery 13.
However, if the revising means 23J revises the residual voltage drop value stored by the storing means 27 in response to the inside or circumferential temperature of the battery 13 when the residual voltage drop value is renewed to the newest residual voltage drop value and the inside or circumferential temperature of the battery 13 when the present estimated voltage of the battery 13 is estimated, since the terminal voltage component corresponding to the inside or circumferential temperature of the battery 13 is reflected in the residual voltage drop value and the estimated voltage under the same condition, the present open circuit voltage can be computed in a condition that the variable component of the terminal voltage due to the difference of the inside or circumferential temperature of the battery 13 is removed by using the revised residual voltage drop value.
Preferably, the first computing means 23A computes the voltage-current characteristic including the influence of the polarization as an approximate curve equation.
With the construction described above, the low pace of the decrease in the voltage drop value of the terminal voltage, which is arisen in the battery 13 due to the polarization by the discharge, is more correctly reflected in the voltage-current characteristic including the influence of the polarization computed by the first computing means 23A, thereby the accuracy of the estimated voltage estimated by the estimating means 23C on the basis of the voltage-current characteristic including the influence of the polarization and the accuracy of the open circuit voltage computed by using the estimated voltage become higher.
Preferably, the current value large enough to cancel a charge-side polarization arisen in the battery 13 at least just before the discharge is a predetermined large current value required to drive a maximum power consuming load 5 independently out of the loads in the vehicle, which receive an electric power from the battery 13, and
after the discharge current of the battery 13 starts decreasing from the predetermined large current value, while the discharge current of the battery 13 is decreasing up to a target current value that is higher than a maximum discharge current value when the loads in the vehicle except the maximum power consuming load 5 are driven, the first computing means 23A computes the voltage-current characteristic including the influence of the polarization from the periodically measured terminal voltage and discharge current of the battery 13.
With the construction described above, the predetermined large current value required to drive the maximum power consuming load independently out of the loads in the vehicle exceeds each current value used for driving the other load even if a plurality of powers are simultaneously supplied to the other loads. Therefore, the predetermined large current value is set to be a current value large enough to cancel the charge-side polarization arisen in the battery 13 at least just before the discharge, thereby when the discharge current reaches the predetermined large current value, a voltage drop exceeding the voltage drop due to the discharge-side polarization arisen by the former discharge is already arisen in the terminal voltage of the battery 13.
On the other hand, when the discharge current value of the battery 13 decreases from the predetermined large current value and reaches to a target current value not less than a maximum discharge current value when the loads except the maximum power consuming load 5 are driven, a voltage drop component due to the discharge-side polarization arisen by the power supply to the loads in the vehicle except the maximum power consuming load 5 does not seemingly affect the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery 13, but a remaining component except a component removed by that the discharge current decreases to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value seemingly affects the voltage drop due to the discharge-side polarization remaining in the terminal voltage of the battery 13.
Consequently, the voltage-current characteristic including the influence of the polarization is computed by the first computing means 23A from the terminal voltage and the discharge current periodically measured while the discharge current of the battery 13, which has carried out the constant load discharge with the predetermined large current value, starts decreasing from the predetermined large current value and reaches the target current value. A present estimated voltage estimated by the estimating means 23C on the basis of the voltage-current characteristic including the influence of the polarization purely reflects only the remaining component except the component canceled due to the decrease of the discharge current decreasing up to the target current value out of the voltage drop due to the discharge-side polarization arisen by the discharge with the predetermined large current value, even if the loads in the vehicle except the maximum power consuming load 5 are still driven.
The present invention is also to provide an apparatus for computing a battery 13 capacity comprising the apparatus for computing an open circuit voltage of a battery 13 as described above, wherein a present charging capacity of the battery 13 is computed from the present open circuit voltage computed by the apparatus for computing an open circuit voltage of a battery 13.
With the construction described above, the present open circuit voltage not including the dispersion due to the difference in the discharge current value or the discharge period of time caused by the voltage fluctuation due to the polarization is used, thereby a present charging capacity of the battery 13, which has a linear relationship with the open circuit voltage, can be computed without including the influence of the voltage fluctuation due to the polarization.
An apparatus for computing the voltage-current characteristic not including the influence of the polarization of the battery or an apparatus for computing the voltage-current characteristic not including the influence of the polarization of the battery in an equilibrium state thereof is not limited to a specific apparatus. Some examples for such an apparatus will be explained as follows.
As for a first apparatus, as shown in FIG. 2, on the basis of the terminal voltage and discharge current periodically measured when the battery 13 carries out the constant load discharge with a current value large enough to cancel the charge-side polarization arisen at least just before the discharge, a first approximate curve equation of the voltage-current characteristic indicating a correlation between the terminal voltage and the discharge current of the battery 13 during the increase of the discharge current and a second approximate curve equation of the voltage-current characteristic indicating a correlation between the terminal voltage and the discharge current of the battery 13 during the decrease of the discharge current are computed by means 23K for calculating the approximate curve equation. Then, a first point is defined on the voltage-current characteristic curve expressed by the first approximate curve equation while a second point is defined on the voltage-current characteristic curve expressed by the second approximate curve. Then, a first imaginary point having the same resistance value as a second combined resistance consisting of a pure resistance of the battery 13 and a second polarization resistance component, which causes a second voltage drop when a second discharge current corresponding to the second point flows, is imaged on the voltage-current characteristic curve expressed by the first approximate curve equation, while a second imaginary point having the same resistance value as a first combined resistance consisting of a pure resistance of the battery 13 and a first polarization resistance component, which causes a first voltage drop when a first discharge current corresponding to the first point flows, is imaged on the voltage-current characteristic curve expressed by the second approximate curve equation. Then, a first gradient of a straight line defined by connecting the second point and the first imaginary point is revised by a quantity corresponding to a voltage drop difference due to the second polarization resistance component arising from the second discharge current and a discharge current at the first imaginary point, thereby a first revised gradient excluding the contribution of the voltage drop due to the second polarization resistance component is computed, while a second gradient of a straight line defined by connecting the first point and the second imaginary point is revised by a quantity corresponding to a voltage drop difference due to the first polarization resistance component arising from the first discharge current and a discharge current at the second imaginary point, thereby a second revised gradient excluding the contribution of the voltage drop due to the first polarization resistance component is computed. Finally, an average gradient is computed by means 23L for computing by addition-averaging the first and second gradients, thereby the average gradient computed by the means 23L for computing is computed as the pure resistance of the battery 13, that is, the voltage-current characteristic not including the influence of the polarization of the battery 13.
With the first apparatus described above, the pure resistance of the battery 13 can be computed only by processing data, obtained by the means 23K for calculating the approximate curve equation, of the terminal voltage and discharge current of the battery 13 periodically measured during the constant load discharge with the predetermined large current.
As for a second apparatus, in addition to the construction of the first apparatus described above, a construction may be employed, in which the first and second points are set as an optional point in a range where the terminal voltage and the discharge current of the battery, which are measured in order to compute the first and second approximate curve equations, exist.
With the second apparatus described above, at least one point for computing the gradient is based on real data, therefore a point significantly missing the real conditions is prevented from being used.
As for a third apparatus, in addition to the construction of the first or second apparatus described above, a construction may be employed, in which the first and second points are set as a point corresponding to the maximum current value of the discharge current of the battery, which is measured in order to compute the first and second approximate curve equations, on the first and second approximate curve equations.
With the third apparatus described above, at least one point for computing the gradient is based on real data, therefore a point significantly missing the real conditions is prevented from being used and in addition, since both points are common, an error is prevented from entering compared to a case, in which the different data are used.
As for a fourth apparatus, in addition to the construction of the first, second or third apparatus described above, a construction may be employed, in which when the first and second approximate curve equations are computed, the periodically measured terminal voltage and discharge current of the battery may be collected for the newest predetermined period of time and stored.
With the fourth apparatus described above, by using the stored real data, the first and second approximate curve equations can be computed after confirming that the discharge current required to compute the first and second approximate curve equations has flowed.